The utilization of dietary protein and energy from diets containing proteins of different qualities at three dietary concentrations will be studied. Diets containing 6, 9, or 12 percent supplied as casein, wheat gluten, whole wheat flour, or isolated soybean protein will be fed for three weeks at different levels of energy intake. The influences of protein source, protein concentration and level of energy intake upon protein and energy utilization from these diets will be assessed. Combining data from the feeding levels, energy depoisition coefficients (change in kcal retained per change in kcal intake) will be determined for total carcass fat and carcass lean for each diet. The change in the energy deposition coefficient for carcass lean relative to that for carcass fat as a function of change in dietary protein concentration will be determined for each protein source. These relationships for the four protein sources will then be compared to determine the influence of protein source and concentrations upon the partitioning of dietary energy for synthesis of fat and lean tissues.